The long-term goal of this research is to elucidate the function of alkaline phosphatases (APs) during development and the significance and utility of their re-expression in cancer and other diseases. The underlying hypotheses are that a) APs have an essential function and b) that tumors acquire a selective advantage by re-expressing AP genes. In fact: a) inactivation of the tissue non-specific AP (TNAP) gene is incompatible with normal life leading to infantile hypophosphatasia and perinatal death and b) consistent re-expression of the human germ cell (GCAP) and placental (PLAP) genes in gonadal tumors is firmly established. Considerable knowledge is now available that the principal investigator believes it timely to advance this field to the translational stage. The present competitive renewal application focuses on using GCAP and PLAP to develop tools that will benefit patients in three important clinical areas: I) In the treatment of hypophosphatasia: GCAP expression constructs ill be tested for their ability to compensate by gene therapy, for the lack of TNAP in our mouse model of hypophosphatasia. The investigators will assay in vitro for bone nodule formation to test the efficacy of the constructs, and use bone marrow transplantation with ex vivo manipulated osteoblast precursor cell to assess the effectiveness of the treatment. The investigators will make use of the GCAP transgenic mice previously developed in our lab which display immunotolerance to GCAP. Breeding of our TNAP knockout mice to the GCAP transgenic mice will render mice that closely mimic the human patient situation, i.e., display a hypophosphatasia phenotype and are immunotolerant to GCAP. The use of GCAP as a therapeutic gene would circumvent the host immune response towards the therapeutic gene product, a problem which often complicates gene therapy trials. II) In the diagnosis of testicular cancer: Dr. Millan and his colleagues will develop a non-invasive, specific method for the detection of carcinoma-in-situ cells in seminal fluid for the early detection of testis cancer. They will use anti-GCAP antibodies in combination with RT-PCR amplification of tumor-specific transcripts to attain the required specificity and sensitivity. III) In the treatment of ovarioan carcinoma: The investigators will develop and use bispecific antibodies directed against GCAP or PLAP on tumor cells and CD3 on the surface of cytotoxic T cells to treat ovarian cancer cells in vitro. These bispecific antibodies will be useful in the treatment of metastatic lesions and residual masses after surgical resection of the bulk of the tumors.